Nuclear LegacyDemocracy in a Plutonium Economy

Corner House Briefing 02

by Frank Barnaby

first published 2 November 1997

Summary

Plutonium is a radioactive by-product of nuclear reactors and one of the most toxic substances known. The nuclear industry argues that it should be mixed with uranium oxide and used in ordinary nuclear reactors as mixed-oxide or MOX fuel elements. Yet this would produce more plutonium; cost more than conventional nuclear fuel; be less safe; increase the risk of serious accidents during transportation; necessitate extreme high security to prevent theft; and increase the risk of nuclear weapon proliferation by countries and terrorist organisations.

Forget Chernobyl! This is far worse", pronounces a White House nuclear scientist (alias Nicole Kidman) in the 1997 movie, The Peacemaker. She has just learnt of a collision in Russia between two trains, one of which was carrying a nuclear warhead from a dismantled nuclear missile. With the drafted-in assistance of action man army colonel George Clooney (from television's ER), Kidman and colleagues discover that another nine warheads on the train have been stolen. They are being trucked overland down to the Iranian border by a Russian general who engineered the heist, the Bosnian buyer of one of the warheads, and a Harvard-trained Pakistani physicist, who separates the fission trigger out of one thermonuclear warhead and makes it into a small bomb which fits neatly into the Bosnian's backpack. After car chases, helicopter downings and a lot of fatal shootings, action man and colleagues recover eight warheads from the truck, while Kidman deduces that the remaining backpack version is on its way to the United Nations in New York with a Bosnian diplomat. Bomb and Bosnian are tracked down. With seconds to spare on the timed device, Kidman bashes away at the conventional explosive surrounding the plutonium core, ensuring that when the explosive goes off, the plutonium will not reach critical mass. The device then blows and Kidman and Clooney are hurled through a stained glass window. An uncontrolled chain reaction in the plutonium -- a nuclear explosion -- has, however, been prevented. The good guys win. All is well. The End.

Unfortunately, in the real world rather than in the movies, this would be just the beginning. Although a nuclear explosion was prevented, the detonation of the conventional explosive would have caused the plutonium sphere in the centre of the device to splinter into millions of tiny radioactive pieces which would be dispersed into the lungs and stomachs of New Yorkers. Inhaled or ingested, these particles could cause the death of hundreds of people within a month, and more still over the next decade or so from lung, stomach, liver and bone cancers. This is the terrorist potential of plutonium as much as its explosive effects.

There have already been a few hundred known incidents of nuclear smuggling, mostly of small quantities not close to weapons grade material1 -- but one gramme of plutonium is more than sufficient to cause significant harm and to pose a substantial threat. The potential for further thefts is growing as the world produces ever more quantities of plutonium, not only from the dismantling of nuclear weapons but also from the separation out of plutonium from spent uranium nuclear reactor fuel elements. Trying to prevent the theft of gramme quantities of plutonium would require levels of protection and surveillance unacceptably high in a democratic society. It is unlikely, therefore, that democracy could survive in a plutonium economy.

Plutonium is a human-made material, produced in nuclear reactors as uranium fuel degrades (see Appendix, below). Only traces occur in nature.

Mainly because of its radioactivity, it is exceedingly toxic -- the inhalation of microgramme quantities has a very high probability of causing fatal lung cancer while the ingestion of plutonium can cause bone and liver cancer. Plutonium contains several radioisotopes, some of them very long-lived; the half-life of plutonium-239, for example, is 24,110 years.2 To all intents and purposes, therefore, plutonium remains permanently in the environment. It is also an extremely efficient explosive.

Plutonium was first discovered in 1941 as part of the Manhattan project, set up in the United States during the Second World War to manufacture nuclear weapons. The bomb dropped on Nagasaki was a plutonium bomb. Since 1945, the world has produced a huge amount of plutonium -- about 1,400 tonnes (see Appendix, below) either in order to manufacture nuclear weapons or as a "by-product" of nuclear power reactors.

There are only two potential significant uses for plutonium: to manufacture nuclear weapons and to fuel nuclear reactors. To obtain plutonium, it has first to be separated out from the spent uranium reactor fuel. Such reprocessing was originally justified during the 1970s on the grounds that there would eventually be a shortage of uranium to fuel nuclear power reactors which could be mined at economic prices. Breeder reactors fuelled by plutonium instead of uranium would have to be developed and used commercially. Several experimental breeder reactors have been built, but have run into a number of technical and economic problems, such that it will be several decades at least before they can be justified economically -- if at all.3

In the meantime, however, the industry argues that plutonium oxide (the form in which plutonium exists after reprocessing) should be mixed with uranium oxide (the form of uranium usually used in reactors) and the mixture used in ordinary reactors as mixed-oxide or MOX fuel elements. The nuclear industry is pressing hard for the large-scale fabrication and widespread use of mixed-oxide fuel because it sees this as one of the few ways of maintaining the lagging momentum of nuclear technology in the West, leading eventually to the widespread commercial use of breeder reactors.4 Six large (commercial-scale) reprocessing plants are currently operating in England, France, Russia and Japan,5 while MOX-fabrication plants are operating or will operate in England, Belgium, France, Japan and Russia.6

Besides providing plutonium oxide for the fabrication of MOX fuel, reprocessing spent reactor fuel elements is also justified as a means of disposing of the embarassingly large pile of nuclear waste.

The production of MOX, however, is illogical. There are several important arguments against using it:

the use of MOX as fuel in reactors produces more plutonium;

there is not a foreseeable shortage of economically-viable uranium, because demand and prices have dropped;

the cost of MOX fuel is much higher than that of normal uranium-oxide fuel;

technical considerations (such as reduced effectiveness of the control rods in absorbing neutrons) may make reactors fuelled by MOX less safe than uranium-fuelled ones;

the use of MOX increases the risk of serious accidents during transportation between reactors, reprocessing plants, MOX fabrication plants and back to reactors;

the need to protect MOX fuel elements kept at nuclear reactors from illegal theft will involve reactor operators in new physical security problems;

international safeguards designed to prevent nuclear proliferation are difficult to enforce at facilities associated with plutonium and MOX; and

the use of MOX increases the risk of nuclear-weapon proliferation by countries and, perhaps more seriously, by terrorist organisations.

These factors are rarely discussed, particularly the last one. The risk of governments or groups being able to manufacture a nuclear bomb illegally is significantly enhanced by the fact that the separation of plutonium from MOX is a straightforward and relatively simple chemical operation.

Some members of terrorist organizations or sub-national groups have access to considerable professional scientific and technical skills and to large sums of money. The construction of the explosive device that destroyed the PanAm jumbo jet over Lockerbie on 21 December 1988, for example, required considerable expertise. So did the nerve gas weapon used in the Tokyo underground by the AUM group on 20 March 1995. The fabrication of a primitive nuclear explosive (as opposed to a military nuclear weapon) requires no greater skill than that required to make either of these.

Access to skills and finance combined with the world's increasing stockpile of available plutonium; the small amounts of plutonium needed for a nuclear explosive; the availability in open literature of the technical information required to design and fabricate such an explosive; and the small number of competent people necessary to manufacture a primitive nuclear explosive are reasons for considerable concern.7

After plutonium has been separated from spent uranium fuel elements in a reprocessing plant, it is usually stored at the reprocessing plants as plutonium oxide powder, the form in which it is most likely to be acquired illegally. It is much simpler to construct a nuclear explosive using plutonium oxide instead of plutonium metal because the oxide is easier and safer to handle. Plutonium metal may burst into flames when it comes into contact with air, for instance.

The disadvantage of plutonium oxide, however, is that its critical mass (the minimum amount of a fissile material that, if struck by neutrons, will result in a self-sustaining chain reaction of the atomic nuclei splitting into two, resulting in a nuclear explosion) is much higher than that of plutonium metal. The critical mass of reactor-grade plutonium (derived from a civilian nuclear power reactor rather than produced for military weapons) in the form of plutonium-oxide crystals is about 35 kilogrammes,8 a sphere of approximately nine centimetres radius, about the size of a football, whereas the critical mass of metallic reactor-grade plutonium of the same grade is 13 kilogrammes (see Appendix, p.11).

In a crude nuclear explosive device, the plutonium oxide could be contained in a spherical vessel placed in the centre of a large mass of a conventional high explosive. A number of detonators could be used to set off the explosive, probably by remote control. The shock wave from the explosion would compress the plutonium oxide sufficiently to produce some energy from nuclear fission.

The size of the nuclear explosion resulting from such a crude device is impossible to predict. Even if it was equivalent to the explosion of only a few tens of tonnes of TNT, it could completely devastate the centre of a large city. The 1996 IRA bombing of Manchester used roughly one and a half tonnes of explosive based on fertilizer and primed with Semtex.9 Such a device would, however, have an excellent chance of exploding with an explosive power of at least one hundred tonnes of TNT.

The largest terrorist explosion so far was equivalent to about two tonnes of TNT. A nuclear explosion equivalent to 100 tonnes of TNT in an urban area would be catastrophic.

Exploded on or near the ground, such an explosion would produce a crater in dry soil or dry soft rock about 30 metres across. For small nuclear explosions -- those with explosive powers of less than a few kilotonnes -- lethal radiation would cover an area larger than that affected by blast and heat. The area of lethal damage from the blast produced by a 100-tonne nuclear explosion would be roughly 0.4 square kilometres (100 acres); the lethal area for heat would be about 0.1 square kilometres (25 acres); while that for radiation would be roughly 1.2 square kilometres (300 acres).10

Persons out in the open at the time of the explosion and within 600 metres of it would probably be killed immediately by the direct effects of radiation, blast or heat. Many other deaths would occur from indirect blast effects -- the collapse of buildings, people being hurled into objects, falling debris and so on. A large number of people would be seriously injured by blast, heat and radiation effects. Heat and blast cause fires from broken gas pipes, petrol in cars, and the like. The area and extent of damage from fire may well exceed those from the direct effects of heat.

A nuclear explosion at or near ground level would also produce a relatively large amount of early radioactive fall-out. Heat from fires would cause the radioactive particles to rise into the air from where they would be blown downwind, eventually falling to the ground under gravity at rates and distances which will depend on the velocity of the wind and the weather conditions. The area significantly contaminated with radioactive fall-out and plutonium would be uninhabitable until decontaminated. Such an area may be many square kilometres and would take a long time to decontaminate to a level sufficiently free of radioactivity to be acceptable to the public. One kilogramme of uniformly-distributed plutonium would contaminate about 600 square kilometres to a radiation level of one micro-curie per square metre, the maximum permissible level allowed for plutonium by international regulations.11 To put in perspective, 600 square kilometres is twice or more the size of all the main urban areas in Britain (Birmingham, Glasgow, Sheffield, Bradford Liverpool, Manchester, Edinburgh, Bristol, Coventry, Belfast and Cardiff) except Greater London at 1,600 square kilometres and Leeds at about 600 square kilometres.

An explosion of this size, involving many hundreds, even thousands, of deaths and injuries, would paralyse the emergency services. They would find it difficult to deal effectively with the dead, let along the injured. Many, if not most, of the seriously injured would not get medical attention in time to save their lives. In the UK, for example, there are only a few hundred burn beds in the whole of the National Health Service. There would be considerable delays in releasing injured people trapped in buildings. It would take a significant time to get ambulances to those not trapped and to transport them to hospital. When large explosions occur in an urban area, the ensuing panic also affects trained emergency personnel, a panic which would be considerably enhanced by the radioactive fall-out accompanying a nuclear explosion.

Just as significant, if not more so, however, would be a crude nuclear device which, when detonated, did not produce a significant nuclear explosion. Such a device could be contained in a van, for instance, and positioned so that the explosion of the conventional high explosives alone would disperse the plutonium widely.

If incendiary materials were mixed with the high explosives, the explosion could be accompanied by a fierce fire. The plutonium would burn in the fire, separating into small particles of plutonium. These would be taken up into the atmosphere in the fire-ball and scattered far and wide downwind. A large number of these particles would be small enough for people to inhale into their lungs or ingest into their gastrointestinal system.

The toxicity of plutonium stems mainly from the ionizing alpha particle radiation it emits as plutonium nuclei decay. If plutonium is ingested or inhaled, such radiation is delivered to various internal organs of the body.12 Inhaled plutonium particles become embedded in the lung and irradiate it; ingested plutonium will irradiate the walls of the gastrointestinal tract. Both ingested and inhaled plutonium may migrate via the blood stream to concentrate selectively in the liver and bones.13 Generally speaking, an intake of a given amount of plutonium is much more hazardous if inhaled than ingested because plutonium is more easily absorbed into the blood stream through the lungs than through the gastrointestinal tract. The long-term (chronic) health effects of this radiation are increased risks of developing cancer of the lung, gastrointestinal tract, liver and skeleton, depending on the route of plutonium intake. The cancers may take up to 25 years to appear.

Short-term (acute) effects are possible after the inhalation or ingestion of larger amounts of plutonium. Evidence for these effects, mainly based on experiments with beagle dogs, suggest that the inhalation of a total of between 10 and 20 milligrammes of reactor-grade plutonium may cause death in humans from acute respiratory failure within one week. The inhalation of two to four milligrammes of reactor-grade plutonium may cause death within about one month from pulmonary fibrosis or pulmonary edema.14

Estimating the impacts on human health of plutonium isotopes is fraught with uncertainties;15 consequently many risk estimates are conservative. Bearing in mind the uncertainties, the best estimates made by the International Commission on Radiological Protection (ICRP) of the fatal cancer risks arising from the inhalation and ingestion of plutonium suggest that reactor-grade (civil) plutonium is much more toxic that weapons-grade (military) plutonium because it contains more plutonium-239. For weapons-grade plutonium, breathing in about 430 microgrammes (millionths of a gramme) will have a very high probability of causing a fatal cancer; for typical reactor-grade plutonium, however, the amount is just one-seventh of this, some 60 microgrammes. By contrast, ingestion of about 30 milligrammes (thousandths of a gramme) of weapons-grade plutonium will have a very high probability of causing a fatal cancer, but just one tenth of this, three milligrammes, is needed for typical reactor-grade plutonium to have the same effect.16

These figures suggest that if individuals in a population inhale a total of one gramme of typical reactor-grade plutonium, there would be about 20,000 extra deaths in the population, while ingestion of a gramme of this type of plutonium would result in nearly 400 extra deaths from cancer. To put these figures into perspective, a spherical piece of plutonium oxide containing one gramme of plutonium has a diameter of 5.5 millimetres (0.22 inch) -- the size of a peppercorn -- and there are 1,400 tonnes of plutonium in the world.

The dispersal of many kilogrammes of plutonium over a city would make a wide area uninhabitable until it could be decontaminated, a procedure which could take many months. The threat of dispersion is perhaps the most serious danger that would arise from the acquisition of plutonium by a terrorist group. This danger is so great that the mere possession of significant quantities of plutonium by a terrorist group is a threat in itself. If a terrorist group proved to a government that it had plutonium in its possession, it would have significant potential for blackmail.

Because of the risk that plutonium may be stolen or otherwise illegally acquired and used to produce nuclear weapons illegally, either by governments or sub-national groups, the question of whether safeguards can be effectively applied to facilities which handle plutonium is critical.

Safeguarding plutonium while it is still in spent reactor uranium fuel elements is relatively simple. All that is required is to count the number of elements in the area in which they are stored, in the cooling pond at the reactor, for example17 -- a matter of unit accountancy plus, possibly, surveillance with video cameras. The safeguarding of fresh MOX reactor fuel elements is more complicated but still possible. But commercial facilities for the bulk handling of plutonium -- specifically, plants for reprocessing plutonium and for the fabrication of MOX fuel elements -- cannot be effectively safeguarded in the same way for several reasons.

The British Thermal Oxide Reprocessing Plant (THORP) at Sellafield, for example, will separate about 7,000 kilogrammes of plutonium a year. The reactor operators which send their spent fuel elements to THORP for reprocessing cannot measure the amount of plutonium in these elements -- they are too radioactive to allow measurements to be taken.

Instead, the operators calculate the amount of plutonium based on their knowledge of how the reactor operated while the fuel elements were in the core -- the heat generated, and so on. Although the reactor operators have not stated the error in their calculations, independent experts estimate it at about five per cent.18 Thus reprocessors do not know for certain how much plutonium they started out with, and without a clear baseline, it is impossible to know what may be missing.

Once separated out, the plutonium is usually stored as plutonium oxide in quantities well below its critical mass in vessels, each of which is locked into its own vault.

Because of these measurement uncertainties and the large amount of plutonium handled in a commercial reprocessing plant, conventional safeguard techniques, such as counting or measuring, are not sufficiently precise to ensure that the diversion of enough plutonium to fabricate a nuclear weapon would be detected in a timely way. This has nothing to do with efficiency or competence. Even using the best available and foreseeable technologies and accountancy techniques, the safeguards on plutonium bulk-handling facilities are ineffective.19 The plants most difficult to safeguard effectively are large reprocessing plants.

Countries operating nuclear facilities try to prevent nuclear thefts and illicit activities not only by operating a safeguards system, but also a physical protection one. The two systems are meant to be complementary: the safeguards system should in theory detect the disappearance of nuclear material if the physical protection system fails to prevent such a disappearance in the first place. The physical protection system should then recover the stolen material. Because it is not possible to safeguard plutonium bulk-handling facilities adequately, the effectiveness of the physical protection of plutonium in such plants is crucially important.

The International Atomic Energy Agency (IAEA) in Vienna has published general recommendations for a national physical protection system for nuclear material which are meant to set minimum standards. Normally, national systems are based on these recommendations. The responsibility for establishing and operating physical protection systems rests solely with the government of the country in which the nuclear facility is operated. The main aids to physical protection are the use of security devices, guards and security procedures, and the limitation of access to significant amounts of nuclear material to a minimum number of people, selected for their trustworthiness.

With the use of MOX, reactors will become stores of weapon-usable plutonium. This will require them to be guarded with much greater thoroughness than they are today and provided with more physical protection with implications for the surveillance of workers on the reactor site.

At least 500 workers enter and leave a large commercial reprocessing plant or MOX fabrication plant daily, providing hundreds of thousands of opportunities each year for the illegal removal of plutonium. The easiest way to obtain plutonium illicitly from such a facility would be to bribe, seduce or blackmail an employee who may otherwise be above suspicion, having a job which requires security clearance to ensure trustworthiness. Security investigations and surveillance would thus have to extend far beyond the worker in the facility or a nuclear transport worker -- family, friends and associates would also be involved.

Given the small amount of plutonium needed to constitute a terrorist threat, the severity of searches and surveillance at a plutonium bulk-handling facility would have to be exceptionally high to deter or detect the theft of gramme quantities of plutonium.

In addition, an emergency force would have to be prepared to recover rapidly any stolen plutonium as soon as the theft is detected. This implies a large force of highly-trained, well-armed commandos with a wide range of detection equipment, including airborne equipment.

Adequately sized and trained teams would also need to be ready to deal with any emergencies arising during the transport of significant amounts of plutonium from the reprocessing plant to MOX fabrication plant, and from the fabrication plant to a nuclear reactor site. The teams should be able to reach the scene of an incident in transit either while the illicit action is in progress or, at worst, immediately afterwards when the possibility of recovering any stolen plutonium is greatest. For this purpose, the emergency teams should be sited at a number of strategic locations within the countries through which nuclear transports pass.

Today's terrorists may be armed with automatic weapons, stand-off missiles and other weapons of great fire-power. An attack on a nuclear transport may, therefore, be a formidable one, requiring an equally-armed or better-armed defensive force to defeat it.

The severity of physical protection measures will inevitably increase as thefts or attempted thefts occur. In time, trade unions, civil liberties and citizen groups will find the protection measures necessary in facilities and for nuclear transportation intolerable. Moreover, the draconian emergency measures eventually adopted to deal with incidents in facilities and during transportation, involving heavily armed guards and commando teams with massive fire-power stationed at many locations, will be intolerable in most democratic societies.

Thus in an open society, operating under the rule of law, it is extremely doubtful whether the procedures required to protect a plutonium economy adequately would be legally, politically and socially acceptable. In short, it is reasonable to question whether a democracy could survive in an economy based on the large-scale use of MOX fuel.

The nuclear industry is looking for ways to keep itself going. It believes that its future lies in clean-up and reprocessing. In addition, as national governments make commitments to combat global warming by reducing carbon dioxide emissions which stem from the burning of coal, oil and gas, the industry believes such governments will have little choice but to prolong the life of existing plants and even commission new ones if they are to meet their commitments. Increasing amounts of plutonium are being removed from nuclear weapons and stored under civilian control, while more and more plutonium from civilian nuclear power reactors is being chemically separated from spent reactor fuel elements in commercial reprocessing plants and kept in civilian plutonium stores.

Because of the impossibility of applying adequate safeguards to plutonium bulk-handling facilities, physical protection is the only real security safeguard to prevent the theft and illegal diversion of plutonium. The severity of physical protection measures would inevitably increase as incidents occur. Most people will find the protection measures necessary in facilities and for plutonium transportation intolerable.

A different future is possible. Given that there are no economically-viable peaceful uses for plutonium -- at least not until breeder reactors are demonstrably able to generate electricity economically, which is unlikely to happen for several decades, if ever -- reprocessed plutonium should be stored or permanently disposed of. In the meantime, all commercial reprocessing plants should be closed down, plutonium should not be separated from spent reactor fuel elements, and there should be a halt to the fabrication of MOX.

Nuclear reactors are fuelled with uranium which is found in the ground and currently mined from Canada, Australia, Niger, Namibia, the United States, Russia, Uzbekistan, South Africa and Kazakstan,

Uranium has two important isotopes -- uranium-235 and uranium-238. Uranium-235 is a fissile isotope: when its nucleus captures a neutron travelling at any speed, it undergoes fission, that is, the nucleus splits into two nuclei, which are called fission products, of different chemical elements; these are mostly highly radioactive and include isotopes such as iodine-131, caesium-137 and strontium-90. The energy released in fission as heat is used to generate electricity.

During fission, two or three neutrons from the original nucleus are also emitted. If one of these emitted neutrons is captured by the nucleus of an atom of the more stable uranium-238, it will only cause fission of the atom if it is travelling at a very high speed. If it is not, a nucleus of the radioactive isotope neptunium-239 will be produced which will decay into plutonium-239, another fissile isotope. Therefore, as the uranium fuel in a reactor undergoes fission, an increasing amount of plutonium-239 is produced.

Plutonium-239 can itself capture neutrons to become plutonium-240, which in turn can capture neutrons to become plutonium-241, and so on. Consequently, a mixture of plutonium isotopes is gradually produced in a nuclear reactor.

There are various grades of plutonium, each with different isotopic compositions, according to the way in which it was produced. Plutonium produced in a commercial or civil reactor, operated for the most economical production of electricity, is called reactor-grade plutonium. Plutonium produced in a military reactor specifically for use in nuclear weapons is called weapons-grade plutonium.

Weapons-grade plutonium contains about 93 per cent of plutonium-239 and about 6 per cent of plutonium-240, whereas reactor-grade plutonium typically contains about 60 per cent of plutonium-239 and about 25 per cent of plutonium-240. To obtain weapons-grade plutonium, the fuel elements are removed from the reactor after a relatively short time, so that there is little build up of plutonium-240 and subsequent isotopes.

When removed from a reactor, a spent fuel element contains unused uranium, fission products and plutonium. These three substances can be chemically separated from each other by dissolving them in nitric acid in a reprocessing plant -- essentially a plutonium-production plant or "plutonium factory". The spent fuel elements can also be stored above ground until they can be permanently and safely disposed of in geological repositories.

Of the 1,400 tonnes of plutonium produced since 1945, nearly one sixth, about 250 tonnes, was produced specifically for use in nuclear weapons. The remaining 1,150 tonnes are civilian plutonium, produced as an inevitable by-product of civilian nuclear power reactors while they are generating electricity.

Five countries have developed nuclear weapons programmes: the United States, the Soviet Union, the UK, France and China. The amount of military plutonium in the United States is about 100 tonnes. The country is currently dismantling about 1,800 nuclear weapons each year, the equivalent of about seven tonnes of plutonium. As of mid-1995, the US had in store the fissile cores of about 8,000 already dismantled nuclear weapons which contain a total of some 32 tonnes of plutonium.

The amount of military plutonium in the former Soviet Union is probably about 130 tonnes. Russia is apparently dismantling about 1,800 nuclear weapons a year, probably containing about seven tonnes of plutonium.

The UK has probably produced about 10 tonnes of military plutonium of which about three tonnes are still in weapons. France may have produced roughly six tonnes of military plutonium. China probably has about two tonnes in its weapons. Israel may have produced about 950 kilogrammes of military plutonium and India between 200 and 300 kilogrammes.

The world's stock of military plutonium is unlikely to increase very much. China, France, the United States and the UK have now stopped producing military plutonium per se. A small amount is still being produced in Russia in three reactors which are also used to generate electricity for domestic heating purposes; they will be shut down when their heating function can be replaced, probably before the end of the 1990s. India and Israel are probably producing military plutonium but in relatively small amounts.

The amount of civil plutonium being produced, however, is increasing significantly. The world's nuclear power reactors currently produce 70 tonnes of plutonium a year. In 1995, a total of 447 reactors were in operation and 39 under construction in 33 countries; nuclear power produces about 17 per cent of the world's electricity. Britain opened the first commercial reactor in 1956 at Calder Hall in Cumbria, based on a civil version of a military plutonium production reactor, the Magnox. Over the next 30 years, however, some 233 reactors will be shut down in western and eastern Europe and the United States as they come to the end of their lives, adding to the pile of waste which has to be dealt with.

About 230 tonnes of civil plutonium have been separated out in reprocessing plants from spent nuclear power reactor fuel elements. By the year 2000, there will be some 300 tonnes of separated civil plutonium; if current reprocessing plans go ahead, there will be about 550 tonnes of separated civil plutonium by the year 2010.

At the turn of this century, about 80 tonnes of civil plutonium will be in France, about 50 tonnes in the UK, the same amount in Japan, and about 40 tonnes each in Germany and Russia. Smaller amounts (less than eight tonnes) will be in each of Belgium, India, Italy, The Netherlands, Spain, Switzerland and the US.

An uncontrolled fission chain reaction -- the capturing of a neutron by atoms of a fissile material such that the nucleus of the atom splits in two, emitting more neutrons -- generates enough energy to produce a large explosion. This reaction is achieved by assembling a quantity of a fissile material, such as plutonium, greater than the critical mass of the material.

The critical mass of a fissile material is the minimum amount of the substance that will result in a self-sustaining fission chain reaction. If a medium such as beryllium surrounds the fissile material, it can efficiently reflect neutrons which have escaped through the surface of the fissile material back into the fissile material, causing further fissions. A neutron reflector thus reduces the critical mass.

A bare sphere of weapons-grade plutonium has a critical mass of 11 kilogrammes. If the sphere is surrounded by a natural uranium reflector about 10 centimetres thick, the critical mass is reduced by more than half to about 4.4 kilogrammes -- a sphere with a 3.6 centimetre radius, about the size of an orange.

The beryllium neutron reflector shell is, in turn, surrounded by a shell of a heavy material such as uranium which acts as a tamper or plug. This is itself surrounded by conventional high explosives, such as HMX. When the high explosives around the tamper are detonated, the shock wave causes the tamper to collapse inwards. Its inertia helps hold the plutonium together during this initial explosion to prevent the premature disintegration of the fissioning material. This initial explosion compresses the sphere of plutonium uniformly, thereby reducing its volume and increasing its density.

The critical mass is inversely proportional to the square of the density. The original less-than-critical mass of fissile material will, after compression, become super-critical, a fission chain reaction will take place and a nuclear explosion will occur.

The complete fission of one kilogramme of plutonium-239 would produce an explosion equivalent to that of 18,000 tonnes of TNT. Modern fission weapons have efficiencies approaching 45 per cent, giving explosive yields equivalent to that of about 7,000 tonnes of TNT per kilogramme of plutonium present.

A typical modern nuclear-fission weapon would use three or four kilogrammes of weapons-grade plutonium, surrounded by an efficient neutron reflector and tamper and about 100 kilogrammes of high explosive. The entire volume of the device would be about that of a football and its total weight roughly 200 kilogrammes.

The critical mass of reactor-grade plutonium is slightly greater than that of weapons-grade plutonium, 13 kilogrammes for a bare metal sphere. Nuclear-weapon designers prefer weapons-grade plutonium to fabricate nuclear weapons. But if it is not available, reactor-grade plutonium can be used effectively, proved when the US exploded such a weapon in 1962.

Reactor-grade plutonium can be converted to weapon-grade plutonium using lasers in a process known as Laser Isotope Separation (LIS). LIS increases the proportion of one isotope in a mixture of isotopes. For example, the concentration of plutonium-239 in reactor-grade plutonium -- which contains a mixture of isotopes (plutonium-238, -239, -240, -241 and -242) -- can be increased to make the reactor-grade plutonium more suitable for the fabrication of nuclear weapons.

An example of this method of separating isotopes is the Atomic Vapor Laser Isotope Separation (AVLIS) system developed by the Lawrence Livermore Laboratory in California which uses copper-vapour and dye lasers to separate the plutonium isotopes.

An AVLIS commercial-scale enrichment plant may be in operation in the US by the late 1990s. The first major industrial scale application will be the production of low-cost enriched uranium to fuel nuclear-power reactors. But the plant could also be used to increase the proportion of plutonium-239 in reactor-grade plutonium for use in nuclear weapons.

LIS research and development is also underway in Russia, France, Japan, Germany, the UK, Israel, China, Brazil and India. The spread of LIS technology has serious consequences for the proliferation of nuclear weapons and the potential for plutonium theft.

3 The core of a breeder reactor, consisting of fissile uranium-235 and plutonium-239 and non-fissile uranium-238, is surrounded by a blanket of uranium-238. The fast neutrons which escape from the core can be captured by the uranium-238 which forms plutonium-239. Breeders have to be cooled with liquid metal, such as sodium, rather than water, which is used in conventional reactors, because water would slow down the neutrons, limiting the number that could cause breeding -- the conversion of uranium-238 to plutonium-239. Liquid sodium, however, is highly inflammable with air and reacts explosively with water; the technology which would allow large quantities of liquid metal to be used safely has not yet been developed. Moreover, breeder reactors which can generate electricity at competitive prices have yet to be developed. Apart from Japan and Russia, therefore, countries are no longer actively interested in breeder reactors. Britain's version at Dounreay in Scotland closed down in 1994, while the largest breeder reactor, Superphénix, near Lyons in France, has been closed for much of its life because of problems with its sodium cooling system.

4 This strategy stems from the fact that the nuclear industry in the West has been in the doldrums for many years now. A combination of the Chernobyl accident, no solution for nuclear waste disposal, and cheaper electricity available from other sources has meant that there are no orders on the books for new reactors in the West. The main new nuclear activity is now concentrated in Asia. China, India, Japan, South Korea, North Korea, Pakistan, and Taiwan are all increasing the number of nuclear power reactors they operate. Given the lack of new orders in the West, the industry relies on servicing existing reactors and refuelling them to make its profits -- replacing spent uranium fuel rods is the biggest share of the orders

5 The reprocessing plants are B205 and THORP at Sellafield, England; the UP2 and UP3 plants at La Hague, France; RT1 at Chelyabinsk, Russia; and one at Tokai-Mura, Japan. A Japanese plant at Rokkasho-Mura is scheduled to start operating soon after the year 2000.

15 The figures used by national authorities, such as the British National Radiological Protection Board (NRPB), and by international authorities, such as the International Commission on Radiological Protection (ICRP), to estimate the cancer risks to human health of exposure to ionising radiation rely mainly on data from the survivors of the 1945 atomic bombings of Hiroshima and Nagasaki. But research on these survivors has not produced a significant amount of accurate or reliable data on the radiation effects on human health. See Roff, S. R., Hotspots: The Legacy of Hiroshima and Nagasaki, Cassell, London, 1995; "Investigations by Scientists of Kyoto University, Hiroshima Atomic Bomb, August 1945 and Super-Hydrogen Bomb test at Bikini Atoll in the mid-Pacific", March 1954, Kyoto Forum, Kyoto, 1995.

16 Barnaby, F., "The Radiological Hazards of Plutonium", Medicine, Conflict and Survival, Vol. 13, 1997, pp.195-206. A recent study suggests that a single alpha particle may be carcinogenic. See International Journal of Radiation Biology, Vol.72, p.515.

17 Even after many years, the fuel elements are so radioactive that they can be handled only with heavy remote-handling equipment.